1. Field of the Invention
The present invention relates to a gas sensor superior in both liquid ingress preventing property and durability. More particularly, it is concerned with a gas sensor having a gas detecting element and a structure which permits the gas sensor itself to be attached to other members and is capable of preventing the ingress of liquid to the gas detecting sensor and improving durability.
2. Discussion of the Background
Heretofore there has been known a concentration cell type gas sensor for detecting a certain kind of gas component contained in the exhaust gases of internal combustion engines or various combustion apparatus. For example, an oxygen sensor for detecting oxygen contained in the exhaust gases of an automobile engines is of a structure which permits the introduction of air (oxygen) into the reference electrode-side interior of an oxygen detecting element. However, in the event of entry of a liquid such as water or oil into the interior of the detecting element, the liquid is vaporized by the heat of the exhaust gases and produces a gas or gases other than oxygen with the result that a required electromotive force is not obtained and it therefore becomes impossible to exactly detect oxygen in the exhaust gases. In an effort to eliminate such an inconvenience, prior art devices utilize a structure as shown in FIG. 1, in which a seal member 6 made of rubber is attached through a spacer 8 to an end portion of a sensor protecting sleeve 4 which is mounted to a metallic body 2, so as to prevent the ingress of liquid such as water or oil into an oxygen detecting element (zirconia element) 10. But, since the exhaust gases from automobiles have fairly high temperatures (about 700.degree.-800.degree. C.), such rubber seal member cannot afford sufficient heat resistance and its life is short.
On the other hand, by using a seal member formed of a heat-resistant synthetic resin, it is possible to improve the heat resistance and prolong the life of such seal member but a satisfactory seal cannot be ensured because of its poor elasticity.